In this Connect & Preserve session, we take a deeper dive into file formats for research data with speaker – and file format expert – Valentijn Gilissen of DANS. Choosing the right file format helps to ensure your data remains usable in the long-term, at the same time helping the interoperability with other datasets and the reusability for others. But how do you know which file format to choose? For example, how to choose between an open file format, which can be easily opened by others and preserves well in the long-term, and a proprietary format that is the most accepted and used format in your discipline? And while checking the ‘preferred file format’ lists produced by, for example, DANS is very helpful in this process, who actually decides which formats are put on this list, and how do they decide?